Early WU microwave equipment

Today I looked at documents in the Western Union collection at the Archives Center of the National Museum of American History, related to the company s first

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, Oct 12, 2000

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Today I looked at documents in the Western Union collection at the Archives
Center of the National Museum of American History, related to the company's
first commercial microwave network, which began operation in 1947.

The material includes a complete manual for the relay and terminal
equipment, which was built by RCA. The basic configuration consisted of
two racks of equipment, which passed an intermediate-frequency signal by
coaxial cable (up to 200 ft. long, I think) to transmitters and receivers
(called "head ends") operating in the 4 GHz band. The head ends were
weatherproof boxes mounted near the antenna and connected to it by a short
(7 ft. max.) coaxial cable. The equipment included a provision for two
receivers on each path, to provide space-diversity protection against
signal fading. The antennas were 4 ft. diameter parabolics.

This configuration appears similar to the Army equipment used on the
Pentagon-Ft.Monroe link of the same era.

The manual says that the typical relay station would use a tower of the
"forestry observation type", 100 ft. tall. The equipment racks would
normally be mounted at ground level for easy access, but could be installed
in a 7 ft. square enclosure at the top of the tower. The cover artwork of
the manual includes a somewhat stylized drawing of such a tower, with the
dishes mounted on the lower part of the cabin atop the tower.

Some time ago, I had seen a Western Union ad offered on eBay, which
included a similar illustration. Due to the fanciful nature of the ad (it
showed yellow WU telegram forms streaming out of the dishes!) I thought at
the time that the station's appearance might be merely an artist's
conception.

But in fact, I think such a tower still exists at the former WU site in
Gambrill State Park, MD, though it lacks the enclosed cabin. It's
currently an FAA microwave relay station.

Albert

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